Challenges for Electricity Distribution

Networks

Dr Stuart Galloway and Dr Simon Gill

Advanced Electrical Systems Group

Institute for Energy and Environment

Department of Electronic and Electrical Engineering

University of Strathclyde

Glasgow G1 1RD

United Kingdom

Stuart.Galloway@strath.ac.uk

Simon.Gill@strath.ac.uk

mailto:stuart.galloway}@strath.ac.ukmailto:stuart.galloway}@strath.ac.uk

• What is the electricity distribution network?

• What impact does DG have on the distribution network?

• Why are some distribution networks ‘Full’ of DG?

• How can other distributed energy resources mitigate

the limitations on DG?

Introduction

WHAT IS THE ELECTRICITY DISTRIBUTION

NETWORK?

The World of Distribution

• large number of medium

and low voltage, lower

value assets

• Radial Systems

predominate

Infrastructure

Scotland it is ≤ 33kV

England and Wales it is ≤132kV

The World of Distribution

• Small transformer

• Limited redundancy

• Hard to automate

• Little real-time control

actions

Infrastructure

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The World of Distribution

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• Limited real time visibility

• Limited options for remote

control

• Some automatic control

actions

• No visibility / control of

lower voltage levels (11kV

and below)

Monitoring and visibility

The World of Distribution

• Highly resistive

• Can have significant

imbalance on three phase

components and …

• large single phase sections

• Often ‘radial’

Electrical characteristics

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The World of Distribution

The network, particularly at lower voltage levels, has

little or no real time monitoring to the point to that it

relies on customers phoning up to report a fault.

Some automated control actions exist, but very limited

remote control is possible.

At lower voltage levels, ‘automatic’ response is likely

to involve simply disconnecting a load / generator /

network section, until an engineer can attend

Summary

Components of a Distribution Network

Components of a Distribution

Network

Grid Supply Point (GSP)

substation:

Joins T and D networks

Multiple transformers and circuits with

redundancy:

If one is off due to fault, the other is not overloaded

Primary Substation

(33kV / 11kV)

Radial 11kV circuits

Secondary

transformers /

substations

(11kV / 400 V)

LV

circuits

Single

phase

Loads

(e.g.

Your

house)

On Load Tap

Changers

WHAT IMPACT DOES

DISTRIBUTED GENERATION

HAVE ON THE DISTRIBUTION

NETWORK?

- It affects the system power flow by providing a

source of energy that can be consumed locally

- Adding DG can improve reliability (helps meet

local demand)

- Adding DG can also decrease reliability if there

is excess power (flexible demand becomes

useful).

- It affects the voltage profile of a distribution

feeder

11kV Feeder

Nominal Voltage

Statutory Limit

Statutory Limit

Operational Limit

Operational Limit

11kV Feeder

Nominal Voltage

Statutory Limit

Statutory Limit

Operational Limit

Operational Limit

WHY ARE SOME DISTRIBUTION

NETWORKS ‘FULL’ OF

DISTRIBUTED GENERATION?

What is Firm capacity?

- the capacity of installed generation that can be operated

whilst keeping the system within operating limits under the

worst case conditions

- Worst case conditions are usually Minimum

demand, Maximum generation e.g. 3AM on a windy, warm summers night.

Traditional + Distributed

Generation

at all times

Beyond the Firm Limit

Beyond the Firm Limit

Traditional + Distributed

Generation

Beyond the Firm Limit

Traditional + Distributed

Generation

Curtail

Curtail

Active

Network Management

Beyond the Firm Limit

Curtail

Curtail

Increase

demand

Charge

Storage

The full

Smart Grid…?

Beyond the Firm Limit

The Active Network Management

Philosophy

- Firm limit means, by definition, there is additional network capacity the vast

majority of the time. But no monitoring and control available to access it securely

- ANM aims to use minimal monitoring and controllability of new generation to

access that network capacity

Monitor key point

(current, Amps)

Monitor output of

‘Non-firm’ generators

Reduce output of

‘non-firm’ generators

if required

HOW CAN OTHER

DISTRIBUTED ENERGY

RESOURCES MITIGATE THE

LIMITATIONS ON DG?

- Energy Storage

- Connection of New Demand

- Commercial

- EV

- Smart metering

- Network visibility

- Complementary Energy

Carriers

- Whole systems approach

- Market/Policy Solutions